From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, page_alloc: inline the fast path of the zonelist iterator
The page allocator iterates through a zonelist for zones that match the
addressing limitations and nodemask of the caller but many allocations
will not be restricted. Despite this, there is always functional call
overhead which builds up.
This patch inlines the optimistic basic case and only calls the iterator
function for the complex case. A hindrance was the fact that
cpuset_current_mems_allowed is used in the fastpath as the allowed
nodemask even though all nodes are allowed on most systems. The patch
handles this by only considering cpuset_current_mems_allowed if a cpuset
exists. As well as being faster in the fast-path, this removes some junk
in the slowpath.
The performance difference on a page allocator microbenchmark is;
4.6.0-rc2 4.6.0-rc2
statinline-v1r20 optiter-v1r20
Min alloc-odr0-1 412.00 ( 0.00%) 382.00 ( 7.28%)
Min alloc-odr0-2 301.00 ( 0.00%) 282.00 ( 6.31%)
Min alloc-odr0-4 247.00 ( 0.00%) 233.00 ( 5.67%)
Min alloc-odr0-8 215.00 ( 0.00%) 203.00 ( 5.58%)
Min alloc-odr0-16 199.00 ( 0.00%) 188.00 ( 5.53%)
Min alloc-odr0-32 191.00 ( 0.00%) 182.00 ( 4.71%)
Min alloc-odr0-64 187.00 ( 0.00%) 177.00 ( 5.35%)
Min alloc-odr0-128 185.00 ( 0.00%) 175.00 ( 5.41%)
Min alloc-odr0-256 193.00 ( 0.00%) 184.00 ( 4.66%)
Min alloc-odr0-512 207.00 ( 0.00%) 197.00 ( 4.83%)
Min alloc-odr0-1024 213.00 ( 0.00%) 203.00 ( 4.69%)
Min alloc-odr0-2048 220.00 ( 0.00%) 209.00 ( 5.00%)
Min alloc-odr0-4096 226.00 ( 0.00%) 214.00 ( 5.31%)
Min alloc-odr0-8192 229.00 ( 0.00%) 218.00 ( 4.80%)
Min alloc-odr0-16384 229.00 ( 0.00%) 219.00 ( 4.37%)
perf indicated that next_zones_zonelist disappeared in the profile and
__next_zones_zonelist did not appear. This is expected as the
micro-benchmark would hit the inlined fast-path every time.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 13 +++++++++++--
mm/mmzone.c | 2 +-
mm/page_alloc.c | 26 +++++++++-----------------
3 files changed, 21 insertions(+), 20 deletions(-)
diff -puN include/linux/mmzone.h~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator include/linux/mmzone.h
--- a/include/linux/mmzone.h~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator
+++ a/include/linux/mmzone.h
@@ -919,6 +919,10 @@ static inline int zonelist_node_idx(stru
#endif /* CONFIG_NUMA */
}
+struct zoneref *__next_zones_zonelist(struct zoneref *z,
+ enum zone_type highest_zoneidx,
+ nodemask_t *nodes);
+
/**
* next_zones_zonelist - Returns the next zone at or below highest_zoneidx within the allowed nodemask using a cursor within a zonelist as a starting point
* @z - The cursor used as a starting point for the search
@@ -931,9 +935,14 @@ static inline int zonelist_node_idx(stru
* being examined. It should be advanced by one before calling
* next_zones_zonelist again.
*/
-struct zoneref *next_zones_zonelist(struct zoneref *z,
+static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
enum zone_type highest_zoneidx,
- nodemask_t *nodes);
+ nodemask_t *nodes)
+{
+ if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))
+ return z;
+ return __next_zones_zonelist(z, highest_zoneidx, nodes);
+}
/**
* first_zones_zonelist - Returns the first zone at or below highest_zoneidx within the allowed nodemask in a zonelist
diff -puN mm/mmzone.c~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator mm/mmzone.c
--- a/mm/mmzone.c~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator
+++ a/mm/mmzone.c
@@ -52,7 +52,7 @@ static inline int zref_in_nodemask(struc
}
/* Returns the next zone at or below highest_zoneidx in a zonelist */
-struct zoneref *next_zones_zonelist(struct zoneref *z,
+struct zoneref *__next_zones_zonelist(struct zoneref *z,
enum zone_type highest_zoneidx,
nodemask_t *nodes)
{
diff -puN mm/page_alloc.c~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-inline-the-fast-path-of-the-zonelist-iterator
+++ a/mm/page_alloc.c
@@ -3192,17 +3192,6 @@ retry:
*/
alloc_flags = gfp_to_alloc_flags(gfp_mask);
- /*
- * Find the true preferred zone if the allocation is unconstrained by
- * cpusets.
- */
- if (!(alloc_flags & ALLOC_CPUSET) && !ac->nodemask) {
- struct zoneref *preferred_zoneref;
- preferred_zoneref = first_zones_zonelist(ac->zonelist,
- ac->high_zoneidx, NULL, &ac->preferred_zone);
- ac->classzone_idx = zonelist_zone_idx(preferred_zoneref);
- }
-
/* This is the last chance, in general, before the goto nopage. */
page = get_page_from_freelist(gfp_mask, order,
alloc_flags & ~ALLOC_NO_WATERMARKS, ac);
@@ -3358,14 +3347,21 @@ __alloc_pages_nodemask(gfp_t gfp_mask, u
struct zoneref *preferred_zoneref;
struct page *page = NULL;
unsigned int cpuset_mems_cookie;
- int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET|ALLOC_FAIR;
+ int alloc_flags = ALLOC_WMARK_LOW|ALLOC_FAIR;
gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
struct alloc_context ac = {
.high_zoneidx = gfp_zone(gfp_mask),
+ .zonelist = zonelist,
.nodemask = nodemask,
.migratetype = gfpflags_to_migratetype(gfp_mask),
};
+ if (cpusets_enabled()) {
+ alloc_flags |= ALLOC_CPUSET;
+ if (!ac.nodemask)
+ ac.nodemask = &cpuset_current_mems_allowed;
+ }
+
gfp_mask &= gfp_allowed_mask;
lockdep_trace_alloc(gfp_mask);
@@ -3389,16 +3385,12 @@ __alloc_pages_nodemask(gfp_t gfp_mask, u
retry_cpuset:
cpuset_mems_cookie = read_mems_allowed_begin();
- /* We set it here, as __alloc_pages_slowpath might have changed it */
- ac.zonelist = zonelist;
-
/* Dirty zone balancing only done in the fast path */
ac.spread_dirty_pages = (gfp_mask & __GFP_WRITE);
/* The preferred zone is used for statistics later */
preferred_zoneref = first_zones_zonelist(ac.zonelist, ac.high_zoneidx,
- ac.nodemask ? : &cpuset_current_mems_allowed,
- &ac.preferred_zone);
+ ac.nodemask, &ac.preferred_zone);
if (!ac.preferred_zone)
goto out;
ac.classzone_idx = zonelist_zone_idx(preferred_zoneref);
_
--
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